Packet mode auto-detection in multi-mode wireless communication system, signal field transmission for the packet mode auto-detection, and gain control based on the packet mode

ABSTRACT

A method for automatically detecting a packet mode in a wireless communication system supporting a multiple transmission mode includes: acquiring at least one of data rate information, packet length information and channel bandwidth information from a transmitted frame; and determining the packet mode on the basis of the phase rotation check result of a symbol transmitted after a signal field signal and at least one of the data rate information, the packet length information and the channel bandwidth information acquired from the transmitted frame.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/044,803, filed on Oct. 2, 2013, now U.S. Pat. No. 9,001,637,which is a continuation of U.S. patent application Ser. No. 12/912,666filed on Oct. 26, 2010, now U.S. Pat. No. 8,582,418 issued on Nov. 12,2013, which claims priority of Korean Patent Application No(s).10-2009-0101925 (and 10-2009-0101956, 10-2010-0006218, 10-2010-0013642),filed on Oct. 26, 2009, (and Oct. 26, 2009, Jan. 22, 2010, Feb. 12,2010, respectively,) which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to packet modeauto-detection in a multi-mode wireless communication system, signalfield transmission for the packet mode auto-detection, and gain controlbased on the packet mode; and, more particularly, to a method forautomatically detecting a packet mode in a multi-mode wirelesscommunication system (e.g., a Wireless Local Area Network (WLAN)communication system supporting various modes) by using a data ratevalue and a packet length setting value, a method for transmitting asignal field for auto-detection of a packet mode by phase rotation of adata tone and/or a pilot tone at the signal field transmission, and amethod for performing an automatic gain control according to thedetected packet mode.

2. Description of Related Art

In general, a wireless communication device based on the IEEE 802.11nstandards uses up to four multiple antennas and a 40 MHz bandwidth andreduces an overhead, thereby making it possible to transmit data at adata rate 10 times higher than a 54 Mbps data rate of a wirelesscommunication device based on the conventional IEEE 802.11a/g standards.Hereinafter, a wireless transmission mode based on the IEEE 802.11a/gstandards will be called a legacy mode, and a wireless transmission modebased on the IEEE 802.11n standards will be called a High Throughput(HT) mode.

An HT signal field HT-SIG is added in an IEEE 802.11n packet in order tomaintain the compatibility with a legacy mode such as IEEE 802.11a/gwhile supporting an HT mode of IEEE 802.11n. The addition of the HTsignal field in the IEEE 802.11n packet is to facilitate thediscrimination from a legacy packet and to process a received signal inconformity with the HT packet frame format.

In general, a legacy transmission frame includes an Orthogonal FrequencyDivision Multiplexing (OFDM) packet preamble, a signal field, and anOFDM data field. For compatibility with the conventional IEEE 802.11a/gstandards, an IEEE 802.11n-based transmission frame includes: a commonpart receivable by both a legacy terminal and a HT terminal; and aHT-dedicated part receivable only by an HT terminal. The common partincludes an OFDM packet preamble (L-STF, L-LTF) and an L-SIG field thatis a signal field for a legacy terminal. The HT-dedicated part includesan HT-SIG1/HT-SIG2 field (i.e., a signal field for an HT terminal), anHT-SIF/HT-LTF field (i.e., a preamble field for an HT terminal), and anOFDM data field.

In such an HT transmission frame structure, a discrimination between alegacy mode and an HT mode is made between L-SIG and HT-SIG. For adiscrimination between a legacy mode and an HT mode, a conventionalmethod transmits an HT signal field by modulating it by a QuadratureBinary Phase Shift Keying (Q-BPSK) scheme that rotates the phase of adata tone of the HT signal field by 90 degrees, as illustrated in FIG.1.

That is, as illustrated in FIG. 1, an HT signal field HT-SIG istransmitted by 90 degree phase modulating a data tone of the HT signalfield HT-SIG in comparison with a legacy signal field L-SIG. Thus, areceiving (RX) terminal can determine whether an HT signal field HT-SIGor a data field for a legacy terminal is received after a legacy signalfield.

However, such a conventional packet mode detection method has a greatdifficulty in discriminating a Q-BPSK modulation signal of an HT signalfield and a 64-QAM modulation signal for data. In order to solve such aproblem, the conventional method discriminates between a 64-QAM signaland a Q-BPSK signal by comparing the accumulation values of the mappedsignal values by using a detection threshold value as illustrated inFIG. 1. However, such a conventional packet mode detection method hasthe following problems.

First, the conventional method is low in terms of the reliability ofpacket mode detection. The method of discriminating between a 64-QAMsignal and a Q-BPK signal by a detection threshold value as illustratedin FIG. 1 is low in terms of a signal-to-noise ratio (SNR) and has ahigh probability that a mode detection error may occur due to a noise ina poor environment with a severe channel change. A 64-QAM signal is themaximum modulation mode in the conventional method, but the problembecomes more serious if the higher modulation scheme (e.g., a 256-QAMmodulation scheme) is used for a very high throughput mode. Therefore, asimple comparison of BPSK and Q-BPSK can be made according to the 6 Mbpsdata rate setting of a legacy signal field, but it is difficult todetect an error in the legacy signal field through a one-bit paritycheck if a channel environment is poor.

Secondly, the conventional method is low in terms of extendibility. Ifthe conventional method is used to discriminate between an HT mode and aVery High Throughput (VHT) mode (the mode following the HT mode) in theHT-SIG, an automatic packet mode detection becomes impossible becausethe I energy and the Q energy become equal in the case of a terminalusing both of the two HT-SIG symbols among the terminals supporting theIEEE 802.11n standards. Accordingly, the total network throughputdecreases and the power consumption efficiency decreases.

The above problems of the conventional method may become more seriouswhen detecting packets based on the Very High Throughput (VHT) wirelesscommunication standards (e.g., IEEE 802.11ac) following the conventionalwireless LAN standards. Hereinafter, the IEEE 802.11ac-based wirelesstransmission mode will be referred to as a VHT mode.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a method forautomatically detecting a packet mode in a wireless communication systemsupporting multi-mode packets, which can perform an automatic packetmode detection with a high reliability while providing a compatibilitywith the conventional method.

Another embodiment of the present invention is directed to a method forautomatically detecting a packet mode in a multi-mode wirelesscommunication system with a high reliability by using a data rate valueand a packet length setting value.

Another embodiment of the present invention is directed to a method fortransmitting a signal field in a multi-mode wireless communicationsystem by using a modulation scheme based on the phase rotation of adata tone and/or a pilot tone, which can implement an automatic packetmode detection with a high reliability while providing a compatibilitywith the conventional method.

Another embodiment of the present invention is directed to a method forautomatically detect a packet mode in a multi-mode wirelesscommunication system by using a different periodicity or a phasedifference of a preamble.

Another embodiment of the present invention is directed to a method forautomatically detecting a packet mode in a multi-mode wirelesscommunication system by using a reserved bit of a signal field L-SIG fora legacy terminal and a reserved bit of a signal field HT-SIG for an HTterminal, which can perform an automatic packet mode detection with ahigh reliability while providing a compatibility with the conventionalmethod.

Another embodiment of the present invention is directed to a method forperforming an automatic gain control in a multi-mode wirelesscommunication system according to the packet mode detected through apacket mode detection process.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art to which the present invention pertains that theobjects and advantages of the present invention can be realized by themeans as claimed and combinations thereof.

In accordance with an embodiment of the present invention, a method forautomatically detecting a packet mode in a wireless communication systemsupporting a multiple transmission mode includes: acquiring at least oneof data rate information, packet length information and channelbandwidth information from a transmitted frame; and determining thepacket mode on the basis of the phase rotation check result of a symboltransmitted after a signal field signal and at least one of the datarate information, the packet length information and the channelbandwidth information acquired from the transmitted frame.

Herein, the data rate information may include at least one of the datarate information HT_RATE for a High Throughput (HT) mode and the datarate information L_RATE for a legacy mode included in the signal fieldof the transmitted frame.

Also, the packet length information may include at least one of thepacket length information HT_LENGTH for a High Throughput (HT) mode andthe packet length information L_LENGTH for a legacy mode included in thesignal field of the transmitted frame.

Also, the signal field may include at least one of the signal fieldL-SIG for a legacy mode and the signal field HT-SIG for a HighThroughput (HT) mode, and the packet mode may be determined by checkingwhether a symbol following the L-SIG signal or the HT-SIG signal is aphase rotation modulation mode.

In accordance with another embodiment of the present invention, a methodfor automatically detecting a packet mode in a wireless communicationsystem supporting a multiple transmission mode includes: acquiring atleast one of data rate information, packet length information andchannel bandwidth information from a transmitted frame; and determiningthe packet mode on the basis of the phase rotation type information of asymbol and at least one of the data rate information, the packet lengthinformation and the channel bandwidth information acquired from thetransmitted frame.

In the packet mode determination, the phase rotation state informationof a symbol following an L-SIG signal that is the signal field for alegacy mode may be additionally used, and the packet mode may bedetermined on the basis of the phase rotation information, the phaserotation state information of the symbol following the L-SIG signal, andat least one of the data rate information, the packet length informationand the channel bandwidth information.

Herein, the data rate information may include at least one of the datarate information HT_RATE for a High Throughput (HT) mode and the datarate information L_RATE for a legacy mode included in the signal fieldof the transmitted frame.

Also, the packet length information may include at least one of thepacket length information HT_LENGTH for a High Throughput (HT) mode andthe packet length information L_LENGTH for a legacy mode included in thesignal field of the transmitted frame.

In accordance with another embodiment of the present invention, a methodfor transmitting a signal field VHT-SIG for a Very High Throughput (VHT)terminal to automatically detect a packet mode in a wirelesscommunication system that transmits a packet frame including a signalfield L-SIG for a legacy terminal and a signal field VHT-SIG for a VeryHigh Throughput (VHT) terminal includes: modulating a symbol of theVHT-SIG field prior to transmission, while rotating the phase of a pilottone and/or a data tone by a predetermined degree in comparison with theL-SIG field.

Herein, the data tone may be rotated by one of 0 degree, 45 degrees, 90degrees and 135 degrees. Also, the pilot tone may be rotated by one of 0degree, 90 degrees, 180 degrees and 270 degrees.

In accordance with another embodiment of the present invention, a methodfor automatically detecting a packet mode in a wireless communicationsystem supporting a multiple mode including a legacy mode for a legacyterminal, a High Throughput (HT) mode for a high throughput terminal,and a Very High Throughput (VHT) mode for a very high throughputterminal includes: receiving a preamble signal for the VHT modemodulated to have a phase difference in comparison with a preamblesignal for the HT mode or a preamble signal for the legacy mode; anddetermining the packet to be the VHT mode packet, if the receivedpreamble signal has a phase difference in comparison with the preamblesignal for the HT mode or the preamble signal for the legacy mode.

In accordance with another embodiment of the present invention, a methodfor automatically detecting a packet mode in a wireless communicationsystem supporting a multiple mode including a legacy mode for a legacyterminal, a High Throughput (HT) mode for a high throughput terminal,and a Very High Throughput (VHT) mode for a very high throughputterminal includes: receiving a preamble signal for the VHT modemodulated to have a periodicity difference in comparison with a preamblesignal for the HT mode or a preamble signal for the legacy mode; anddetermining the packet to be the VHT mode packet, if the receivedpreamble signal has a periodicity difference in comparison with thepreamble signal for the HT mode or the preamble signal for the legacymode.

In accordance with another embodiment of the present invention, a methodfor automatically detecting a packet mode in a wireless communicationsystem supporting a multiple mode including a legacy mode for a legacyterminal, a High Throughput (HT) mode for a high throughput terminal,and a Very High Throughput (VHT) mode for a very high throughputterminal includes: setting the value of a reserved bit for a signalfield of the legacy mode and the value of a reserved bit for a signalfield of the HT mode for definition of the legacy mode, the HT mode orthe VHT mode; and determining the packet mode by using the reserved bitvalue for the signal field of the legacy mode and the reserved bit valuefor the signal field of the HT mode.

In accordance with another embodiment of the present invention, a methodfor transmitting signal information for a Very High Throughput (VHT)mode in a wireless communication system supporting a multiple modeincluding a Very High Throughput (VHT) mode for a very high throughputterminal and at least one of a legacy mode for a legacy terminal and aHigh Throughput (HT) mode for a high throughput terminal includes:disposing a VHT signal field for the VHT mode after a legacy signalfield for the legacy mode or an HT signal field for the HT mode andconstructing a frame in which a portion of signal information for theVHT mode is recorded in a portion of the legacy signal field or aportion of the HT signal field; and transmitting the constructed frame.

In accordance with another embodiment of the present invention, a methodfor automatic gain control in a wireless communication system supportinga multiple mode including a Very High Throughput (VHT) mode for a veryhigh throughput terminal and at least one of a legacy mode for a legacyterminal and a High Throughput (HT) mode for a high throughput terminalincludes: calculating a gain value for automatic gain control; detectinga packet mode of a received packet; determining whether to perform again control by the calculated gain value or by using a short preamble,according to the packet mode detection result; and performing anautomatic gain control on the basis of the determination result.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a conventional packet mode detectionmethod.

FIG. 2 is a flow diagram illustrating a method for detecting a packetmode by using L-SIG information and HT-SIG information in accordancewith an exemplary embodiment of the present invention.

FIG. 3 is a flow diagram illustrating a method for detecting a packetmode by using L-SIG information in accordance with an exemplaryembodiment of the present invention.

FIG. 4 is a flow diagram illustrating a method for detecting a packetmode by using HT-SIG information in accordance with an exemplaryembodiment of the present invention.

FIG. 5 is a flow diagram illustrating a method for detecting a packetmode by using L-SIG information and phase rotation type information inaccordance with an exemplary embodiment of the present invention.

FIG. 6 is a flow diagram illustrating a method for detecting a packetmode by using bandwidth information, L-SIG information and HT-SIGinformation in accordance with an exemplary embodiment of the presentinvention.

FIG. 7 is a flow diagram illustrating a method for detecting a packetmode by using bandwidth information and phase rotation state informationin accordance with an exemplary embodiment of the present invention.

FIG. 8 is a flow diagram illustrating a method for detecting a packetmode by using bandwidth information, L-SIG information and phaserotation type information in accordance with an exemplary embodiment ofthe present invention.

FIG. 9 is a diagram illustrating a VHT mode frame structure.

FIG. 10 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 180-degree phase rotation of apilot tone in accordance with an exemplary embodiment of the presentinvention.

FIG. 11 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 90-degree phase rotation of a pilottone and a data tone in accordance with an exemplary embodiment of thepresent invention.

FIG. 12 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 90-degree phase rotation of a datatone and 270-degree phase rotation of a pilot tone in accordance with anexemplary embodiment of the present invention.

FIG. 13 is a diagram illustrating a process for detecting a packet modethrough signal field transmission without phase shift of a data tone inaccordance with an exemplary embodiment of the present invention.

FIG. 14 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 135-degree phase rotation of a datatone in accordance with an exemplary embodiment of the presentinvention.

FIG. 15 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 135-degree phase rotation of a datatone and 180-degree phase rotation of a pilot tone in accordance with anexemplary embodiment of the present invention.

FIG. 16 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 45-degree phase rotation of a datatone and 180-degree phase rotation of a pilot tone in accordance with anexemplary embodiment of the present invention.

FIG. 17 is a diagram illustrating a process for detecting a packet modethrough signal field transmission by 180-degree phase rotation of apilot tone in accordance with an exemplary embodiment of the presentinvention.

FIG. 18 is a diagram illustrating a method for automatically detecting aVHT mode in a mixed field mode in accordance with an exemplaryembodiment of the present invention.

FIG. 19 is a diagram illustrating a method for automatically detecting aVHT mode in a mixed greenfield mode in accordance with an exemplaryembodiment of the present invention.

FIG. 20 a diagram illustrating a method for redefining/using HT-SIG2 forVHT in accordance with an exemplary embodiment of the present invention.

FIG. 21 is a flow diagram illustrating the location of HT-STF in alegacy/HT mixed mode and the location of VHT-SIGA in a legacy/HT/VHTmixed mode for detailed gain control in accordance with an exemplaryembodiment of the present invention.

FIG. 22 is a flow diagram illustrating a method for detecting a packetmode by phase rotation of a signal field in accordance with an exemplaryembodiment of the present invention.

FIG. 23 is a flow diagram illustrating a method for detecting a packetmode by using phase rotation type information in accordance with anexemplary embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present inventionto those skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The foregoing objects and advantages of the present invention will bedescribed below in detail with reference to the accompanying drawings sothat the technical concept of the present invention can be easilyrealized by those skilled in the art to which the present inventionpertains. In the following description, detailed descriptions ofwell-known functions or configurations will be omitted in order not tounnecessarily obscure the subject matters of the present invention.Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

The present invention provides a method for automatically detecting apacket mode in a wireless communication system supporting a multiplemode. The following description is made in the context of a wirelessLAN, to which the present invention is not limited. Thus, those skilledin the art will readily understand that the present invention may alsobe applicable to any other wireless communication system that uses amulti-mode packet. The terms ‘legacy’, ‘High Throughput (HT)’, and ‘VeryHigh Throughput (VHT)’ used herein to describe the present invention arenot intended to designate specific modes, but are merely exemplary termsintended to represent packets of different modes in a wireless LAN for abetter understanding of the present invention. Thus, those skilled inthe art will readily understand that these terms may be replaced byother terms.

In general, a legacy mode signal field L-SIG has a Rate value L_RATE asa data rate value and has a Length value L_LENGTH as a packet lengthvalue. Also, an HT mode signal field HT-SIG has an MCS (Modulation andCoding Scheme, HT_RATE) value as a data rate value and has an HT_LENGTHvalue as a packet length value.

What is also provided is a technology for preventing a channel access oflegacy terminals at HT mode packet transmission while an HT mode packetoccupies a channel. This is called an L-SIG TXOP protection technologyusing the L_LENGTH and L_RATE of L-SIG. A packet length part and a datarate of an L-SIG field are set for channel occupation time setting foreach of RTS, CTS and DATA packets.

In order to maintaining the compatibility with the conventional IEEE802.11a/g wireless LAN and prevent a signal collision due to aconventional wireless LAN device, the IEEE 802.11n wireless LANtechnology sets a data rate to 6 Mbps and sets a packet length inconformity with the channel occupation period of a transmission (TX)packet. That is, L_RATE and L_LENGTH values are set as “L_RATE=6 Mbps”,“L_LENGTH Value of L-SIG=L_RATE×L SIG Duration”.

Herein, the channel occupation time of a TX packet is determinedaccording to the data rate information and the packet length informationof VHT-SIG or HT-SIG. That is, the channel occupation time of a TXpacket of an HT mode packet is “HT_LENGTH/HT_RATE”, and the channeloccupation time of a TX packet of a VHT mode packet is “VHT LENGTH/VHTRATE”.

A Network Allocation Vector (NAV) value is determined according to thechannel occupation time of the TX packet, the known preamble signal andthe signal field transmission time. That is, the NAV value is determinedto be “aPreambleLength+aPLCPHeaderLength+L-SIG Duration−TXTIME”. Herein,aPreambleLength has a “L-STF+L-LTF” value as a legacy preambletransmission time, and aPLCPHeaderLength means a time necessary forL-SIG transmission. Also, L-SIG Duration has a “L_LENGTH/L_RATE” valueas the channel occupation time of a TX packet, and TXTIME means a timenecessary for packet transmission. HT-SIG Duration or VHT-SIG Durationmay also be calculated in the same way as described above. In general,terminals failing to acquire the channel occupation right sets the NAVvalue to the sum of an L-SIG duration value and a preamble and signalfield transmission time value.

In order to improve the throughput of a VHT mode and maintain thecompatibility, the present invention provides a method for transmittinga VHT mode packet by setting HT_RATE to MCS0. On the basis of the abovecharacteristics, the present invention performs an automatic packet modedetection process in the following manner.

1) A legacy mode or HT mode or VHT mode packet if L_RATE is set to 6Mbps.

2) A legacy mode packet if L_RATE is not 6 Mbps.

3) An HT mode or VHT mode packet if L_LENGTH is greater than a thresholdvalue 1.

4) A legacy mode packet if L_LENGTH is smaller than a threshold value 1.

5) An HT mode packet or a VHT mode packet if HT_RATE is set to MCS0.

6) An HT mode packet if HT_RATE is not MCS0.

7) A VHT mode packet if HT_LENGTH is greater than a threshold value 2.

8) An HT mode packet if HT_LENGTH is smaller than a threshold value 2.

FIG. 2 is a flow diagram illustrating a method for detecting a packetmode by a phase shift by using L-SIG information and HT-SIG informationin accordance with an exemplary embodiment of the present invention.

Although FIG. 2 illustrates the case of using both L_RATE and L_LENGTHsimultaneously, the case of using only one of the two conditions is alsopossible. Also, although FIG. 2 illustrates the case of using HT_RATEand HT_LENGTH conditions simultaneously, one of the two conditions maybe used. A detailed method for this will be described below in detail.

A threshold value 1 and a threshold value 2 may be set by a programmableregister. Because a legacy mode packet does not exceed a 2346-bytelength, the threshold value is set to 2346 bytes as a default value.Also, because an HT mode packet exceeds a 65536-byte length in the eventof aggregation, the threshold value 2 is set to 65537 bytes.

Referring to FIG. 2, if L_RATE is not set to 6 Mbps (in step S201), itis determined to be a legacy mode packet. If L_RATE is set to 6 Mbps (instep S201), the method compares L_LENGTH and the threshold value 1 (stepS202). If the L_LENGTH is smaller than the threshold value 1, the methoddetermines whether the tone in a symbol following an L-SIG field isphase-rotated (step S203).

If the tone in a symbol following an L-SIG field is not phase-rotated,it is determined to be a legacy mode packet. If the tone in a symbolfollowing an L-SIG field is phase-rotated, the method determines whetherHT_RATE is set to MCS0 (step S204). If the L_LENGTH is greater than thethreshold value 1, the method determines whether HT_RATE is set to MCS0(step S204).

If HT_RATE is not set to MCS0 (step S204), it is determined to be an HTmode packet. If HT_RATE is set to MCS0 (step S204), the method comparesthe HT_LENGTH and the threshold value 2 (step S205). If the HT_LENGTH issmaller than the threshold value 2, the method determines whether thetone in a symbol following an HG-SIG field is phase-rotated (step S206).If the tone in a symbol following an HG-SIG field is not phase-rotated,it is determined to be an HT mode packet. If the tone in a symbolfollowing an HG-SIG field is phase-rotated, it is determined to be a VHTmode packet. If the HT_LENGTH is greater than the threshold value 2, itis determined to be a VHT mode packet.

In FIG. 2, if the L_RATE is not used, the method performs an operationof comparing the L_LENGTH and the threshold value 1; and if the L_LENGTHis not used, the method performs the step S203 after the step S201.Likewise, if the HT_RATE is not used, the method performs an operationof comparing the HT_LENGTH and the threshold value 2; and if theHT_LENGTH is not used, the method performs the step S206 after the stepS204.

FIG. 3 is a flow diagram illustrating a method for detecting a packetmode by a phase shift by using L-SIG information in accordance with anexemplary embodiment of the present invention.

Although FIG. 3 illustrates the case of using the L_RATE and theL_LENGTH simultaneously, only one of the two conditions may be used.

Referring to FIG. 3, if the L_RATE is not set to 6 Mbps (step S301), itis determined to be a legacy mode packet. If the L_RATE is set to 6 Mbps(step S301), the method compares the L_LENGTH and the threshold value 1(step S302). If the L_LENGTH is smaller than the threshold value 1, themethod determines whether the tone in a symbol following the L-SIG fieldis phase-rotated (step S303).

If the tone in a symbol following the L-SIG field is not phase-rotated,it is determined to be a legacy mode packet. If the tone in a symbolfollowing the L-SIG field is phase-rotated (step S303), the methoddetermines whether the tone in a symbol following the HT-SIG field isphase-rotated (step S304).

If the tone in a symbol following the HT-SIG field is not phase-rotated,it is determined to be an HT mode packet. If the tone in a symbolfollowing the HT-SIG field is phase-rotated, it is determined to be aVHT mode packet.

In FIG. 3, if the L_RATE is not used, the method performs an operationof comparing the L_LENGTH and the threshold value 1; and if the L_LENGTHis not used, the method performs the step S303 after the step S301.

FIG. 4 is a flow diagram illustrating a method for detecting a packetmode by a phase shift by using HT-SIG information in accordance with anexemplary embodiment of the present invention.

Although FIG. 4 illustrates the case of using the HT_RATE and theHT_LENGTH simultaneously, only one of the two conditions may be used.

Referring to FIG. 4, if the L_RATE is not set to 6 Mbps (step S401), itis determined to be a legacy mode packet. If the L_RATE is set to 6 Mbps(step S401), the method determines whether HT_RATE is set to MCS0 (stepS402).

If HT_RATE is not set to MCS0 (step S402), it is determined to be an HTmode packet. If HT_RATE is set to MCS0 (step S402), the method comparesthe HT_LENGTH and the threshold value 2 (step S403). If the HT_LENGTH issmaller than the threshold value 2, the method determines whether thetone in a symbol following an HG-SIG field is phase-rotated (step S404).

If the tone in a symbol following an HG-SIG field is not phase-rotated,it is determined to be an HT mode packet. If the tone in a symbolfollowing an HG-SIG field is phase-rotated, it is determined to be a VHTmode packet. Also, if the HT_LENGTH is greater than the threshold value2, it is determined to be a VHT mode packet.

In FIG. 4, if the HT_RATE is not used, the method performs an operationof comparing the HT_LENGTH and the threshold value 2; and if theHT_LENGTH is not used, the method performs the step S404 after the stepS402.

FIGS. 2 to 4 illustrate methods for detecting a packet mode by a phaseshift on the basis of the packet length information or the data rateinformation of the signal field. However, the packet mode may also bedetected by using the packet length information and the data rateinformation of the signal field according to a phase shift type.

FIG. 5 is a flow diagram illustrating a method for detecting a packetmode by using packet length information and data rate information of asignal field according to a phase shift type in accordance with anexemplary embodiment of the present invention.

Referring to FIG. 5, if the L_RATE is not set to 6 Mbps (step S501), itis determined to be a legacy mode packet. If the L_RATE is set to 6 Mbps(step S501), the method compares the L_LENGTH and the threshold value 1(step S502). If the L_LENGTH is smaller than the threshold value 1, themethod determines whether the tone in a symbol following the L-SIG fieldis phase-rotated (step S503).

If the tone in a symbol following the L-SIG field is not phase-rotated,it is determined to be a legacy mode packet. If the tone in a symbolfollowing the L-SIG field is phase-rotated (step S503), the methoddetermines whether it is a VHT mode phase rotation type (step S504).Also, if the L_LENGTH is greater than the threshold value 1, the methoddetermines whether it is a VHT mode phase rotation type (step S504).

If it is a VHT mode phase rotation type (step S504), it is determined tobe a VHT mode packet. If it is not a VHT mode phase rotation type but anHT mode phase rotation type (step S505), it is determined to be an HTmode. If it is not an HT mode phase rotation type (step S505), it isdetermined to be an initialization mode or a legacy mode.

Meanwhile, the 802.11a/g mode (legacy mode) can support up to 20 MHz,and the 802.11n mode (HT mode) can support up to 40 MHz, and the VHTmode can support up to 80 MHz. Thus, on the basis of these facts, thepresent invention may determine a packet mode in the following manner.

1) A legacy mode packet or an HT mode packet or a VHT mode packet for a20 MHz channel mode packet.

2) An HT mode packet or a VHT mode packet for a 40 MHz channel modepacket.

3) A VHT mode packet for a 80 MHz channel mode packet.

FIGS. 6 and 7 are flow diagrams illustrating a method for detecting apacket mode by a phase shift by using channel information in accordancewith an exemplary embodiment of the present invention. A wireless LANdevice may detect the bandwidth of a received signal through a carriersensing circuit, and this operation is performed using a preamblefollowed by a signal field of the received signal. That is, not only theaforesaid data rate information and packet length information but alsophase shift information may be detected as the channel bandwidthinformation of a TX signal to detect a packet mode.

FIG. 6 is a flow diagram illustrating a method for detecting a packetmode by a phase shift by using both the signal field information and thechannel information in accordance with an exemplary embodiment of thepresent invention. FIG. 7 is a flow diagram illustrating a method fordetecting a packet mode by a phase shift by using only the channelinformation in accordance with an exemplary embodiment of the presentinvention.

Although FIGS. 6 and 7 illustrate the case of determining whether it isa 20 MHz bandwidth or a 40 MHz bandwidth, only one of the two conditionsmay be used.

Referring to FIG. 6, if the channel bandwidth is determined to be 20 MHzby using a preamble (step S601), the method determines whether theL_RATE is set to 6 Mbps (step S602). If the L_RATE is not set to 6 Mbps(step S602), it is determined to be a legacy mode packet. If the L_RATEis set to 6 Mbps (step S602), the method compares the L_LENGTH and thethreshold value 1 (step S603). If the L_LENGTH is smaller than thethreshold value 1, the method determines whether the tone in a symbolfollowing the L-SIG field is phase-rotated (step S604).

If the tone in a symbol following the L-SIG field is not phase-rotated,it is determined to be a legacy mode packet. If the tone in a symbolfollowing the L-SIG field is phase-rotated, the method determineswhether the HT_RATE is set to MCS0 (step S606).

Also, if the channel bandwidth is determined to be 40 MHz by using apreamble (step S605), the method determines whether the HT_RATE is setto MCS0 (step S606). If the channel bandwidth is determined to be not 40MHz by using a preamble (step S605), it is determined to be a VHT modepacket.

On the other hand, if the HT_RATE is not set to MCS0 (step S606), it isdetermined to be an HT mode packet. If the HT_RATE is not set to MCS0(step S606), the method compares the HT_LENGTH and the threshold value 2(step S607). If the HT_LENGTH is smaller than the threshold value 2, themethod determines whether the tone in a symbol following the HT-SIGfield is phase-rotated (step S608).

If the tone in a symbol following the HT-SIG field is not phase-rotated,it is determined to be an HT mode packet. If the tone in a symbolfollowing the HT-SIG field is phase-rotated, it is determined to be aVHT mode packet. Also, if the HT_LENGTH is greater than the thresholdvalue 2 (step S607), it is determined to be a VHT mode packet.

Although FIG. 6 illustrates the case of using both of the L_RATE and theL_LENGTH and using both of the HT_RATE and the HT_LENGTH, only one ofthe two conditions may be used as described with reference to FIG. 2.

Referring to FIG. 7, if the channel bandwidth is determined to be 20 MHzby using a preamble (step S701), the method determines whether the tonein a symbol following the L-SIG field is phase-rotated (step S702).

If the tone in a symbol following the L-SIG field is not phase-rotated(step S702), it is determined to be a legacy mode packet. If the tone ina symbol following the L-SIG field is phase-rotated (step S702), themethod determines whether the tone in a symbol following the HT-SIGfield is phase-rotated (step S704).

If the tone in a symbol following the HT-SIG field is not phase-rotated(step S704), it is determined to be an HT mode packet. If the tone in asymbol following the HT-SIG field is phase-rotated (step S704), it isdetermined to be a VHT mode packet.

Meanwhile, if the channel bandwidth is determined to be 40 MHz by usinga preamble (step S703), the method determines whether the tone in asymbol following the HT-SIG field is phase-rotated (step S704). If thechannel bandwidth is determined to be not 40 MHz by using a preamble(step S703), it is determined to be a VHT mode packet.

FIG. 8 is a flow diagram illustrating a packet mode detection method inaccordance with an exemplary embodiment of the present invention when aVHT compatible part follows the L-SIG.

Like the case of FIG. 7, the case of FIG. 8 may not use the packetlength information or the data rate information of the signal fieldinformation.

Referring to FIG. 8, if the channel bandwidth is determined to be 20 MHzby using a preamble (step S801), the method determines whether theL_RATE is set to 6 Mbps (step S802). If the L_RATE is not set to 6 Mbps(step S802), it is determined to be a legacy mode packet. If the L_RATEis set to 6 Mbps (step S802), the method compares the L_LENGTH and thethreshold value 1 (step S803).

If the L_LENGTH is smaller than the threshold value 1, the methoddetermines whether the tone in a symbol following the L-SIG field isphase-rotated (step S804). If the tone in a symbol following the L-SIGfield is not phase-rotated (step S804), it is determined to be a legacymode packet.

If the tone in a symbol following the L-SIG field is phase-rotated (stepS804), the method determines whether it is a VHT mode phase rotationtype (step S806). Also, if the L_LENGTH is greater than the thresholdvalue 1 (step S803), the method determines whether it is a VHT modephase rotation type (step S806).

Also, if the channel bandwidth is determined to be 40 MHz by using apreamble (step S805), the method determines whether it is a VHT modephase rotation type (step S806). If the channel bandwidth is determinedto be not 40 MHz by using a preamble (step S805), it is determined to bea VHT mode packet.

On the other hand, if it is a VHT mode phase rotation type (step S806),it is determined to be a VHT mode packet. If it is not a VHT mode phaserotation type but an HT mode phase rotation type (step S807), it isdetermined to be an HT mode packet. If it is not an HT mode phaserotation type (step S807), it is determined to be an initialization modeor a legacy mode.

A description has been given of a method for automatically detecting apacket mode according to the signal field information and the channeltype information. Hereinafter, a description will be given of a methodfor automatically detecting a packet mode by rotating a pilot toneand/or a data tone of a signal field.

FIG. 9 is a diagram illustrating a frame structure for a VHT mode thatis under discussion by IEEE 802.11 TGac for a VHT mode wireless LANservice.

As illustrated in FIG. 9, a VHT frame includes a legacy and/or HTcompatible part and a VHT compatible part or a VHT mode. The legacyand/or HT compatible part includes a short legacy preamble L-SF, a longlegacy preamble L-LTF, and a legacy signal field L-SIG. Also, the legacyand/or HT compatible part may selectively include HT signal fieldsHT-SIG1 and HT-SIG2. The VHT compatible part includes: a VHT-SIGA fieldthat is a signal field receivable by all of legacy mode terminals, HTmode terminals and VHT mode terminals; a VHT-LTF field, a VHT-SIGBfield; a VHT data field; and a VHT-STF field receivable only by VHT modeterminals.

In order to automatically detect a packet mode in the multi-mode packetframe structure, the present invention provides a data tone phasemodulation transmission scheme and/or a pilot tone phase modulationtransmission scheme.

Hereinafter, a description will be given of packet mode detectionmethods using phase rotation of a data tone and/or a pilot tone inaccordance with various exemplary embodiments of the present invention.In the drawings, for convenience in description, a data tone isrepresented by a circle and a pilot tone with a value of −1 or +1 isrepresented by an asterisk.

In FIGS. 10 to 13, a conventional IEEE 802.11a/g signal field L-SIGmodulates a data tone and a pilot tone by a BPSK modulation scheme priorto transmission. Also, an IEEE 802.11n signal field HT-SIG modulates apilot tone by a BPSK scheme prior to transmission and modulates a datatone by a Q-BPSK modulation scheme. Accordingly, a packet mode may bedetected by detecting whether the phase of a field following an L-SIGfield is rotated.

FIG. 10 is a diagram illustrating a method for detecting a packet modethrough signal field transmission by phase rotation of a pilot tone inaccordance with an exemplary embodiment of the present invention.

Referring to FIG. 10, in order to improve the detection reliability ofthe conventional L-SIG field or HT-SIG field and maintain thecompatibility, the present invention provides a method of modulating adata tone of a VHT-SIG field by a 90-degree phase-rotated Q-BPSKmodulation scheme and transmitting a pilot tone by 180-degree phaserotation. If the VHT-SIG field is modulated prior to transmission asillustrated in FIG. 10, the terminal can detect a packet mode throughthe VHT-SIG field, because a data tone has a 90-degree phase differenceand a pilot tone has a 180-degree phase difference in comparison withthe L-SIG field. Also, if the VHT-SIG field is modulated prior totransmission, the receiving terminal can detect a packet mode with ahigh reliability due to a 180-degree phase difference of a pilot tone,which must be extracted before a data tone for phase error estimation,in comparison with the HT-SIG field.

The modulation scheme of the VHT-SIG field illustrated in FIG. 10 may beexpressed as Equation 1.

$\begin{matrix}{{r_{{HT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{HT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{1}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {- 26}}^{26}{\left( {{j\; D_{k,n}} + {p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}{r_{{VHT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{VHT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{{VHT} - {SIG}_{mixindex}}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {tone}_{\min}}^{{tone}_{\max}}{\left( {{j\; D_{k,n}} + {p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

FIG. 11 is a diagram illustrating a method for automatically detecting apacket mode through signal field transmission by phase rotation of apilot tone and phase rotation of a data tone in accordance with anotherexemplary embodiment of the present invention.

In comparison with the exemplary embodiment of FIG. 10, the exemplaryembodiment of FIG. 11 uses a method of modulating a pilot tone by90-degree phase rotation, not by 180-degree phase rotation. That is, theexemplary embodiment of FIG. 11 modulates both of the data tone and thepilot tone for the VHT-SIG field by 90-degree phase rotation.

If the VHT-SIG field is modulated prior to transmission as illustratedin FIG. 11, the receiving terminal can detect a packet mode with a highreliability, because the data tone has a 90-degree phase difference andthe pilot tone has a 90-degree phase difference in comparison with theL-SIG field and the pilot tone has a 90-degree phase difference incomparison with the HT-SIG field.

The modulation scheme of the VHT-SIG field illustrated in FIG. 11 may beexpressed as Equation 2.

$\begin{matrix}{{r_{{HT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{HT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{1}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {- 26}}^{26}{\left( {{j\; D_{k,n}} + {p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}{r_{{VHT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{VHT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{{VHT} - {SIG}_{mixindex}}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {tone}_{\min}}^{{tone}_{\max}}{\left( {{j\; D_{k,n}} + {j\; p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

FIG. 12 is a diagram illustrating a method for automatically detecting apacket mode through signal field transmission by phase rotation of adata tone and phase rotation of a pilot tone in accordance with anotherexemplary embodiment of the present invention.

In comparison with the exemplary embodiment of FIG. 11, the exemplaryembodiment of FIG. 12 uses a method of modulating a pilot tone by270-degree phase rotation, not by 90-degree phase rotation. That is, theexemplary embodiment of FIG. 12 modulates the data tone of the VHT-SIGfield by 90-degree phase rotation and modulates the pilot tone of theVHT-SIG field by 270-degree phase rotation.

If the VHT-SIG field is modulated prior to transmission as illustratedin FIG. 12, the receiving terminal can detect a packet mode with a highreliability, because the data tone has a 90-degree phase difference andthe pilot tone has a 270-degree phase difference in comparison with theL-SIG field and the pilot tone has a 270-degree phase difference incomparison with the HT-SIG field.

The modulation scheme of the VHT-SIG field illustrated in FIG. 12 may beexpressed as Equation 3.

$\begin{matrix}{{r_{{HT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{HT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{1}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {- 26}}^{26}{\left( {{j\; D_{k,n}} + {p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}{r_{{VHT} - {{SIG}{(t)}}}^{irx} = {\frac{1}{\sqrt{N_{TX}N_{{VHT} - {SIG}}^{Tone}}}{\sum\limits_{n = 0}^{{VHT} - {SIG}_{mixindex}}{{w_{T_{SYM}}\left( {t - {nT}_{SYM}} \right)}{\sum\limits_{k = {tone}_{\min}}^{{tone}_{\max}}{\left( {{j\; D_{k,n}} + {j\; p_{n + 1}P_{k}}} \right){\exp \left( {j\; 2\pi \; k\; {\Delta_{F}\left( {t - {n\; T_{SYM}} - T_{GI} - T_{CS}^{irx}} \right)}} \right)}}}}}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

FIG. 13 illustrates a method of modulating the data tone in the samemanner as the L-SIG and modulating only the pilot tone by 90-degreephase rotation, 180-degree phase rotation, or 270-degree phase rotation.FIG. 3A illustrates the case of rotating only the pilot tone by180-degree phase rotation. FIG. 13B illustrates the case of rotatingonly the pilot tone by 90-degree phase rotation. FIG. 13C illustratesthe case of rotating only the pilot tone by 270-degree phase rotation.

If the VHT-SIG field is modulated prior to transmission as illustratedin FIG. 13, the receiving terminal can detect a packet mode with a highreliability, because the pilot tone has a 180-degree phase difference, a90-degree phase difference and a 270-degree phase difference incomparison with the L-SIG field and the data tone has a 90-degree phasedifference and the pilot tone has a 180-degree phase difference, a90-degree phase difference and a 270-degree phase difference incomparison with the HT-SIG field.

In general, because the data tone has no directionality, it may bephase-rotated by 45 degrees (or 135 degrees), by 90 degrees, or by 180degrees (or 0 degree). Also, because the pilot tone has directionality,it may be phase-rotated by 90 degrees, by 180 degrees, or by 270degrees.

There are two cases where limited use is available. The first case isthat the data tone is 0 degree and the pilot tone is 0 degree. In thecase of a frame structure where the VHT-SIG field follows the HT-STFfield or the HT-LTF field, this first method may not be used because itis the same as the data field. However, this first method may also beused in the case of a frame structure where the VHT-SIG field followsthe HT-SIG field or the L-SIG field. The second case is that the datatone is 90 degrees and the pilot tone is 0 degree. In the case of aframe structure where the VHT-SIG field follows the L-SIG field, thissecond method may not be used because it is the same as the modulationscheme of the HT-SIG field. However, this second method may be used inthe case of a frame structure where the VHT-SIG field follows the HT-SIGfield or the HT-STF field or the HT-LTF field.

In general, the IEEE 802.11n-based packet has an HT-SIG field followedby an HT-STF field. Thus, in the case of a VHT mode frame structurewhere a VHT-SIG field follows an HT-SIG field, it is necessary todiscriminate between a VHT-SIG signal and an HT-STF signal of an HTmode.

FIGS. 14 and 15 are diagrams illustrating a method for detecting apacket mode in a VHT frame structure in which a VHT-SIG field follows anHT-SIG field in accordance with an exemplary embodiment of the presentinvention.

Referring to FIG. 14, the present invention modulates a pilot tone inthe same manner as the conventional L-SIG field and modulates a datatone by 135-degreed phase rotation. The reason for the 135-degreed phaserotation of a data tone is that it can provide a detection thresholdvalue capable of detecting an HT-STF signal and a VHT-SIG signal with ahither reliability because an HT-STF signal is mapped to 1+j or −1−j.That is, by comparing the distribution of RX signals by x=0, y=0, if theRX signals are distributed more in the first quadrant (I value >0, Yvalue >0) or in the third quadrant (I value <0, Y value <0), the signalmay be determined to be an HT-SIG signal; and if the RX signals aredistributed more in the second quadrant (I value <0, Y value >0) or inthe fourth quadrant (I value >0, Y value <0), the signal may bedetermined to be an VHT-SIG signal.

The present invention of FIG. 14 can accurately discriminate between anHT-STF signal and a VHT-SIG signal before the processing of thecorresponding symbol by a DFT method because the location of a carrierfrequency for a signal is known by the characteristics of the HT-STF.The present invention of FIG. 14 is applicable if the HT-SIG is used inthe same manner as the conventional HT mixed mode. Also, the method ofmaintaining 90-degree phase rotation or 0 degree rather than 135-degreephase rotation is more efficient in terms of accuracy in the structurewhere a VHT-SIG field follows an L-SIG field without an HT-SIG fieldinterposed therebetween.

Meanwhile, the present invention may simultaneously use the 135-degreephase rotation of a data tone and the phase rotation of a pilot tone inorder to improve the detection reliability. FIG. 15 illustrates the caseof rotating the phase of a data tone by 135 degrees and rotating thephase of a pilot tone by 180 degrees. The present invention includesrotating the phase of a pilot tone by 90 degrees, rotating the phase ofa pilot tone by 180 degrees, and rotating the phase of a pilot tone by270 degrees.

Meanwhile, the present invention includes a method for automaticallydetecting a packet mode by using a data tone with a 90-degree or45-degree phase difference and a 180-degree phase inverted pilot tone.Herein, the discrimination between a VHT-SIG signal and an HT-SIG signalis performed using the 90-degree phase difference of a data tone and the180-degree phase difference of a pilot tone. Also, the discriminationbetween a VHT-SIG signal and an HT-LTF signal is performed using the180-degree phase difference of a pilot tone and the 45-degree phasedifference of a data tone. Also, the discrimination between a VHT-SIGsignal and an HT-SIG (or L-SIG) signal is performed using the 180-degreephase difference of a pilot tone and the 45-degree phase difference of adata tone.

The use of the present invention can support an HT/VHT mixed greenfieldmode. Accordingly, a preamble overhead can be reduced and HT-SIGspoofing is possible. Also, it is possible to perform a signal fielddecoding operation more robust against a noise by using 8-bit CRC. Also,it is possible to secure a very long transmission opportunity using a16-bit length. Also, it is possible to perform an automatic VHTdetection operation using an HT-SIG rate field.

Before describing the features of the present invention, the followingabbreviations are described first.

L denotes a subcarrier of a lower band, and U denotes a subcarrier of anupper band. LD denotes a data subcarrier of a lower band, and UD denotesa data subcarrier of an upper band. LP denotes a pilot subcarrier of alower band, and UP denotes a pilot subcarrier of an upper band. Whendefining a 20 MHz band mode in a wireless LAN, it is divided into alower band, an upper band and a center band. The lower band is a bandlower than a 40 MHz band. The upper band is a band higher than the 40MHz band. The center band is a 20 MHz band having a center frequency atthe center of the 40 MHz band. The 20 MHz center band mode may use thesame method as the 20 MHz lower band mode.

FIG. 16 illustrates a method of performing a modulation operation by45-degree (upper band) or 135-degree (lower band) phase rotation of adata tone for each band (in comparison with the BPSK modulation scheme)and 180-degree phase rotation of a pilot tone in accordance with anexemplary embodiment of the present invention. Herein, the 45-degree and135-degree phase rotation for each band the 45-degree phase rotation foreach band in comparison with the Q-BPSK modulation result.

FIG. 17 illustrates a method of modulating a data tone in the samemanner as the BPSK modulation scheme (i.e., no phase rotation) andmodulating only a pilot tone by 180-degree phase rotation in accordancewith an exemplary embodiment of the present invention.

FIG. 18 is a diagram illustrating a method for automatically detecting aVHT mode in a mixed mode in accordance with an exemplary embodiment ofthe present invention.

In FIG. 18, in the case of a legacy/HT/VHT mixed mode packet, acomparison target is a legacy/HT mixed mode packet. Therefore, acomparison target for automatic detection is the VHT-SIGA of thelegacy/HT/VHT mixed mode packet and the HT-STF and HT-LTF of thelegacy/HT mixed mode packet. As described above, an automatic modedetection for the first symbol of the VHT-SIGA is performed by using a45-degree phase rotation modulation scheme of a data tone and a180-degree phase rotation modulation scheme of a pilot tone. Anautomatic mode detection for the second symbol of the VHT-SIGA isperformed by using the 45-degree phase difference of a data tone and the180-degree phase difference of a pilot tone.

FIG. 19 is a diagram illustrating a method for automatically detecting aHT/VHT mode in a greenfield mode in accordance with an exemplaryembodiment of the present invention.

If an HT-SIG field is included in an VHT frame structure, it can supportan HT/VHT mixed greenfield mode. The comparison target of an HT/VHTmixed greenfield mode packet is an HT greenfield mode. The reason forthis is that the VHT can consider a network environment having only a HTmode and a VHT mode in an environment without a legacy terminal becausethe green field of the conventional IEEE 802.11n standards means anetwork state without a legacy terminal. Herein, because an HT terminalof the IEEE 802.11n standards cannot support an VHT mode, it may performa transmission in an HT greenfield mode. Therefore, the HT/VHT mixedgreenfield mode must automatically detect a packet mode in comparisonwith the HT greenfield mode.

Like the aforesaid VHT-SIGA modulation scheme, the comparison target ofa modulated signal is the HT-LTF. Herein, a VHT mode and an HT mode arediscriminated by a 45-degree phase-rotated data tone and a 180-degreephase-rotated pilot tone. Herein, in the case of an IEEE 802.11nterminal, an automatic mode detection may be performed using both of thetwo symbols of the HT-SIG. However, in the case of a VHT terminal, amode detection must be performed on a symbol basis for detailed gaincontrol of a legacy/HT/VHT mixed greenfield mode.

Specifically, the detailed gain control must be performed on a symbolbasis because whether to reflect the calculated detailed gain value mustbe determined according to the automatic packet mode detection result.The VHT-SIGA of the HT/VHT mixed greenfield mode packet is compared withthe HT-LTF of the HT greenfield mode, but the HT-LTF of the HTgreenfield mode must be detected on a symbol basis because it can be onesymbol.

Recently, the IEEE 802.11 TGac standardization conference is intended todefine the VHT-SIGA by two symbols. However, when it is intended toprovide the use as an information field to be applied to all users andto define various high-end technologies, it may be short of a 2-symbollength. An exemplary embodiment of the present invention includes anHT-SIG field, and it may be redefined/used for a VHT terminal by reusinga portion of the HT-SIG. To this end, a shared signal field S-SIG isused.

FIG. 20 a diagram illustrating a method for redefining/using HT-SIG2 forVHT in accordance with an exemplary embodiment of the present invention.

FIG. 20 illustrates that the HT-SIG2 is redefined/used for the VHT.Likewise, a portion of the HT-SIG is redefined/used for the VHT in thelegacy/HT/VHT mixed mode or the HT/VHT mixed greenfield mode, so thatthe advantages (high-reliability signal demodulation, automatic packetmode detection using HT-SIG information, the possibility of setting avery long transmission opportunity guard interval, and the possibilityof supporting the HT/VHT greenfield mode) of the HT-SIG can be usedwithout increasing the number of symbols of the VHT-SIG.

For example, for Smoothing(1), Sounding(1), Reserved(1), Aggregation(1),STBC(2), FEC coding(1), Short GI(1) and Number of extension spatialstreams(2), a numeral in the parenthesis may be reused for the VHT asbit number information, and additional bits may be allocated to theVHT-SIG.

If the VHT-SIGA is defined in a two-symbol length, it may be used likethe option 1 of FIG. 20. In this case, the greenfield mode can bedetected by detecting a 45-degree phase-modulated Q-BPSK signal at theVHT-SIGA field location and detecting a 180-degree phase-inverted pilot.

In addition, another method of the present invention is a rapid modeautomatic detection method for the VHT greenfield mode. In the case ofVHT-GF-STF, it is a method of performing a transmission by 90-degreephase rotation in comparison with the conventional L-STF or HT-GF-STF.By doing so, the detection of the VHT greenfield mode can be performedimmediately after the automatic detection of the VHT-GF-STF.

FIG. 21 is a flow diagram illustrating the location of HT-STF in alegacy (Le)/HT mixed mode and the location of VHT-SIGA in a legacy(Le)/HT/VHT mixed mode for detailed gain control in accordance with anexemplary embodiment of the present invention.

As illustrated in FIG. 21, because the location of the VHT-SIGA in alegacy (Le)/HT/VHT mixed mode is the same as the location of the HT-STFin a legacy/HT mixed mode, a VHT terminal must determine whether toperform a detailed gain control. The detailed gain control is performedin the following manner.

After a large gain is controlled in the L-STF, a greenfield (GF)/mixedfield (MF) mode is automatically detected in the L-SIG and an HT mode isautomatically detected in the HT-SIG1. Then, RX signal level measurementand gain calculation are performed for detailed gain control in thefirst symbol of the VHT-SIGA. Concurrently, the phase of a data tone andthe phase of a pilot tone are calculated, and a packet mode isautomatically detected before the end of the first symbol of theVHT-SIGA (more specifically, allowing a stabilization time for gaincontrol). If a phase-inverted pilot is present in the first symbol ofthe VHT-SIGA as described above or a 90-degree phase-modulated data toneis detected, it is identified as a VHT mode. Herein, a mode recheck isperformed at the second symbol of the VHT-SIGA without applying thecalculated detailed gain control value. On the other hand, if aphase-inverted pilot is not present in the first symbol of the VHT-SIGAand a 90-degree phase-modulated data tone is not detected, it isidentified as an HT mode. Herein, the calculated detailed gain controlvalue is applied to shift to an HT-LTF reception state. In this manner,the present invention can effectively perform the automatic detectionand the detailed gain control.

As described above, the present invention determines the packet to be aVHT mode packet, when detecting the data tone phase rotation of a signalfollowing a legacy mode or HT mode signal field or an HT mode preamblesymbol. Also, the present invention determines the packet to be a VHTmode packet, when detecting the pilot tone phase rotation of a signalfollowing a legacy mode or HT mode signal field or an HT mode preamblesymbol.

FIGS. 22 and 23 are flow diagrams illustrating a method for detecting apacket mode according to the present invention described above.

FIG. 22 illustrates a method for detecting a packet mode by determiningthe phase shift of a pilot tone and a data tone of the aforesaid signalfield in a frame structure where an L-SIG field, an HT-SIG field and aVHT-SIG field are sequentially located.

Referring to FIG. 22, if the phase rotation is not detected in thesymbol following the L-SIG field (step S2201), it is determined to be alegacy mode packet. If the phase rotation is detected in the symbolfollowing the L-SIG field and if the phase rotation is not detected inthe symbol following the HT-SIG field (step S2202), it is determined tobe an HT mode packet. If the phase rotation is detected in the symbolfollowing the L-SIG field (step S201) and if the phase rotation isdetected in the symbol following the HT-SIG field (step S2202), it isdetermined to be a VHT mode packet.

FIG. 23 a method for identifying an HT mode or a VHT mode according tothe phase shift type in a frame structure where a VHT-SIG field directlyfollows an L-SIG field.

Referring to FIG. 23, if the phase shift is not detected in the symbolfollowing the L-SIG field (step S2301), it is determined to be a legacymode packet. If the phase shift is detected in the symbol following theL-SIG field, the mode is determined according to the phase rotation typeof a VHT mode or an HT mode determined according to the degree of thedata phase shift and the pilot phase shift (steps S2302 and S2303).

Meanwhile, in the case of a frame structure where a sequence with aspecific pattern is inserted after a legacy field (L-SIG or HT-SIG), thepresent invention may detect a packet mode in the following manner.

The preamble following the L-SIG field is a short preamble, which isinserted for a fine automatic gain control of an RX packet operating ina multi-antenna mode. However, according to the correlation calculationresult using the repetitiveness of a preamble, it can be determinedwhether a VHT part or a data field is allocated after an L-SIG field.Also, if an HT-SIG field follows an L-SIG field and a preamble followsan HT-SIG field, it must be determined whether it is an HT mode or a VHTmode. To this end, the determination may be made by using the VHT-STFhaving a different phase from the HT-STF. That is, by using the90-degree, 180-degree or 270-degree phase-shifted VHT-STF of the HT-STFor by varying the periodicity thereof, it can be detected whether thepacket is a VHT mode packet or an HT mode packet. This method may beincluded in the phase difference-based packet mode detection method ofFIG. 23, but differs from the packet mode detection method of FIG. 23 inthat it detects a packet mode by using a preamble instead of a signalfield.

Meanwhile, the present invention includes a method of detecting a packetmode by using a reserved bit of the L-SIG and the HT-SIG. Each of theL-SIG and the HT-SIG includes a 1-bit reserved bit, and the presentinvention includes a method of setting a reserved bit to ‘1’ fortransmission in order to accurately inform whether the packet is an HTmode packet or a VHT mode packet.

A detailed embodiment thereof will be described in the context of thecase where a frame is constructed in the order of L-SIG, HT-SIG andVHT-SIG.

In the first method, if the reserved bit of the L-SIG is ‘1’, the packetis determined to be an HT mode packet; and if the reserved bit of theL-SIG is ‘0’, the packet is determined to be a legacy mode packet. Also,if the reserved bit of the HT-SIG is ‘1’, the packet is determined to bea VHT mode packet; and if the reserved bit of the HT-SIG is ‘0’, thepacket is determined to be an HT mode packet.

In the second method, if the reserved bit of the L-SIG is ‘1’, thepacket is determined to be a VHT mode packet; and if the reserved bit ofthe L-SIG is ‘0’, the packet is determined to be an HT mode packet.Also, if the reserved bit of the HT-SIG is ‘1’, the packet is determinedto be a VHT mode packet; and if the reserved bit of the HT-SIG is ‘0’,the packet is determined to be an HT mode packet.

A description will be given of a frame structure where a VAHT-SIG fieldfollows an L-SIG field without an HT-SIG field interposed therebetween.

If the reserved bit of the L-SIG is ‘1’, the packet is determined to bea VHT mode packet; and if the reserved bit of the L-SIG is ‘0’, thepacket is determined to be a legacy mode packet.

As described above, the method of using the reserved bit of the L-SIG orthe HT-SIG can further improve the packet mode detection accuracy whenused simultaneously with the aforesaid various packet mode detectionmethods.

The above-described methods can also be embodied as computer programs.Codes and code segments constituting the programs may be easilyconstrued by computer programmers skilled in the art to which theinvention pertains. Furthermore, the created programs may be stored incomputer-readable recording media or data storage media and may be readout and executed by the computers. Examples of the computer-readablerecording media include any computer-readable recoding media, e.g.,intangible media such as carrier waves, as well as tangible media suchas CD or DVD.

Because the conventional packet mode detection method must detect apacket mode by a limited number of data tones before decoding an HTsignal field HT-SIG, the reliability and stability of the packet modedetection depends greatly on the hardware processing speed of areceiving terminal. Also, in the case of the conventional method fordiscriminating between a legacy mode data field signal and an HT signalfield (HT-SIG) signal, packet mode detection becomes difficult as themodulation scheme approaches 64-QAM. Also, the accuracy decreases as thenoise becomes serious.

The present invention can detect a packet mode according to the channeltype, the packet length and the data rate of the signal field whilemaintaining the compatibility with the conventional technology.

When transmitting a VHT mode packet, the present invention sets the datarate of a legacy signal field and an HT signal field to the lowest datarate mode. Also, the present invention uses the packet lengthinformation to enable a conventional HT terminal to protect a VHT packetand uses this to make it possible to detect a VHT mode packet. Also,unlike the conventional method, the present invention uses a 40 MHz ormore channels to transmit a VHT packet and provides a multi-channeltransmission through nonadjacent channels, thus making it possible todetermine whether the packet is a legacy mode packet or a VHT modepacket, by using the channel information detected through carriersensing.

Also, in order to detect a packet mode with a high reliability whilemaintaining the compatibility with the conventional technology, thepresent invention rotates the data tone and the pilot tone whentransmitting the VHT signal field VHT-SIG following the HT signal field.Also, the present invention can provide a packet mode detection not onlyby using a signal field but also by using a preamble.

For automatic packet mode detection, the signal field modulation methodaccording to the present invention includes all the possiblecombinations as the modulation scheme using the phase rotation of apilot tone and a data tone in order to solve the reliability problem ofthe conventional method. That is, the present invention modulates asignal field VHT-SIG for a VHT terminal prior to transmission by usingone of the combinations of the case of rotating the phase of a data toneby 45 degrees (or 135 degrees), by 90 degrees, or by 180 degrees (or 0degree) and the case of rotating the phase of a pilot tone by 0 degree,by 90 degrees, by 180 degrees, or by 270 degrees, thereby making itpossible to detect a packet mode with a high reliability.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A method for receiving control information in awireless communication system, the method comprising: receiving a firstmodulation sequence in a first orthogonal frequency divisionmultiplexing (OFDM) symbol; receiving a second modulation sequence in asecond OFDM symbol; and receiving a third modulation sequence in a thirdOFDM symbol, wherein the first modulation sequence is generated bymodulating a signal field on a first binary phase shift keying (BPSK)constellation, wherein the second modulation sequence is generated bymodulating a first Very High Throughput-Signal (VHT-SIG) field on thefirst BPSK constellation; wherein the third modulation sequence isgenerated by modulating a second VHT-SIG field on a second BPSKconstellation, wherein the second BSPK constellation is rotated by 90°counter-clockwise relative to the first BPSK constellation, and whereinthe first OFDM symbol is contiguous with the second OFDM symbol and thesecond OFDM symbol is contiguous with the third OFDM symbol.
 2. Themethod of claim 1, wherein the first OFDM symbol precedes the secondOFDM symbol and third OFDM symbol.
 3. The method of claim 1, wherein thefirst VHT-SIG field includes information indicating whether space timeblock code is used, and the second VHT-SIG field includes informationindicating whether short guard interval is used.
 4. The method of claim1, wherein the first modulation sequence, the second modulation sequenceand the third modulation sequence are received in a bandwidth that isone of 20 MHz, 40 MHz, 80 MHz and 160 MHz.
 5. A device for receivingcontrol information in a wireless communication system, the devicecomprising: a processor; and a memory operatively coupled with theprocessor and storing instructions that when executed by the processorcauses to the device to: receive a first modulation sequence in a firstorthogonal frequency division multiplexing (OFDM) symbol; receive asecond modulation sequence in a second OFDM symbol; and receive a thirdmodulation sequence in a third OFDM symbol, wherein the first modulationsequence is generated by modulating a signal field on a first binaryphase shift keying (BPSK) constellation, wherein the second modulationsequence is generated by modulating a first Very High Throughput-Signal(VHT-SIG) field on the first BPSK constellation; wherein the thirdmodulation sequence is generated by modulating a second VHT-SIG field ona second BPSK constellation, wherein the second BSPK constellation isrotated by 90° counter-clockwise relative to the first BPSKconstellation, and wherein the first OFDM symbol is contiguous with thesecond OFDM symbol and the second OFDM symbol is contiguous with thethird OFDM symbol.
 6. The device of claim 5, wherein the first OFDMsymbol precedes the second OFDM symbol and third OFDM symbol.
 7. Thedevice of claim 5, wherein the first VHT-SIG field includes informationindicating whether space time block code is used, and the second VHT-SIGfield includes information indicating whether short guard interval isused.
 8. The device of claim 5, wherein the first modulation sequence,the second modulation sequence and the third modulation sequence arereceived in a bandwidth that is one of 20 MHz, 40 MHz, 80 MHz and 160MHz.